Cook noodles in a large pot of boiling water until al dente. Drain.
Meanwhile prepare the sauce. Heat oil in a medium saucepan over medium heat. Add onions, and ham if desired. Cook until onion is transparent, 2 to 3 minutes. Add garlic, and cook for 30 seconds. Stir in thawed spinach. Mix in sour cream, cream of celery soup, and Parmesan cheese. Reduce heat to low, and heat through.
Serve spinach sauce over spaghetti or egg noodles.